1. Field of the Invention
The present invention relates to digital video recording and playback apparatus. More particularly, the present invention relates to the structure of a digital video recording and playback apparatus, namely, a digital audio tape recorder (hereinunder referred to as "DAT") which is applied to a still picture filming apparatus.
2. Description of the Related Art
FIG. 6 shows an example of the structure of a DAT.
This apparatus has the following structure. An analog/digital converter (hereinunder referred to as "A/D converter") 1, a memory 2, an interleaving circuit 3 and a digital recording portion 4 are connected in series, and the digital recording portion 4 is connected to a recording head 6 which is in contact with a digital audio tape 5. A playback head 7 which is in contact with the digital audio tape 5 is connected in series to a digital playback portion 8, a memory 9, a de-interleaving circuit 10 and a digital/analog converter (hereinunder referred to as "D/A converter") 11.
The operation of this apparatus will now be explained.
The operation of recording a signal into the digital audio tape 5 will first be explained.
In this case, an analog audio signal is inputted to the A/D converter 1 so as to be converted into a digital audio signal. The digital audio signal outputted from the A/D converter 1 is stored in the memory 2. The memory 2 has a storage capacity of, for example, about 128 kbits.
The digital audio signal stored in the memory 2 is read out to the interleaving circuit 3. The interleaving circuit 3 subjects the digital audio signal to an interleave processing. The interleave processing is generally a processing for intermittently recording a pair of digital signals so as to avoid lumped recording of the signals. For example, this processing enables digital signals to be corrected and compensated at the time of playback against the generation of continuous errors due to the defect, flaws, etc. of a digital audio tape (corresponding to the digital audio tape 5 in FIG. 6) on which the digital signals are recorded.
The digital audio signal subjected to the interleave processing is supplied to the digital recording portion 4 and recorded on the digital audio tape 5 through the recording head 6.
The operation of playing back the digital audio signal from the digital audio tape 5 will be explained in the following.
When the digital audio signal is played back from the digital audio tape 5 through the playback head 7 by the playback portion 8, the digital audio signal is stored in the memory 9. The memory 9 has a storage capacity of about 128 kbits.
The digital audio signal stored in the memory 9 is supplied to the de-interleaving circuit 10. The de-interleaving circuit 10 releases the digital audio signal from the interleave processing given by the interleaving circuit 3 at the time of recording. The digital audio signal is supplied from the de-interleaving circuit 10 to the D/A converter 11 to be converted into an analog audio signal and is outputted to an analog signal processor.
When such a DAT is used as a still picture filming apparatus, the storage capacities of the memories 2, 9 are insufficient. For example, an NTSC standard picture (resolution: 640 horizontal dots.times.480 vertical lines) is written in the memory 2 at real time. The picture read out of the memory 2 is recorded on the digital audio tape 5. The storage capacity of the memory 2 is insufficient for storing the digital signals relating to the picture.
In addition, when the digital signals relating to the picture are recorded on the digital audio tape 5, various formats may be adopted in the present state of art, but it is difficult for the structure of the apparatus shown in FIG. 6 to correspond to a plurality of formats.
When digital signals relating to a still picture are played back from the digital audio tape 5 and supplied to an external apparatus such as in the case of dubbing, it is necessary to deteriorate the picture quality to a certain extent for the protection of copyright or the like. Such treatment is impossible in a conventional apparatus.